In mining and construction, wear members are typically provided along the digging edge of the equipment to protect the bucket or the like and/or to engage and break up the ground to be gathered. Accordingly, the wear parts are subjected to highly abrasive conditions and experience considerable wearing. The wear parts must then be replaced on a periodic basis.
In order to minimize the loss of material due to replacement of worn parts, the wear assemblies are typically manufactured as two or more separable components including an adapter and a wear member. The adapter is attached to the digging edge by welding, mechanical attachment, or being cast along an edge of the excavating device so as to present a forwardly projecting nose for supporting the wear member. The wear member has a socket that is received over the nose, and a forward working end. In a point, the working end is typically a narrowed digging edge. The wear member substantially envelops the adapter nose and thereby tends to protect the nose from wear. For example, depending on a variety of factors, generally five to twenty points can be successively mounted on a single adapter before the adapter becomes worn and in need of replacement. To accommodate replacement of the wear member in the field, the wear member is usually secured to the adapter nose by a removable lock (e.g., a lock pin).
Wear assemblies used in mining, excavation and construction, and particularly excavating tooth systems, are subjected to large and varied forces applied in all directions. As a result, points and other wear members must be firmly secured to the adapter to withstand the axial, vertical, reverse and lateral loads as well as impacts, vibrations and other kinds of forces. Vertical loads have been particularly troublesome in that large moment forces are generated that tend to “rotate” the wear members forward on the adapter and at times result in the ejection of the member. While the walls of the adapter nose provide support for the wear member, the lock in most cases also plays a large role in retaining the point and resisting loads, particularly moment and reverse forces.
In a conventional tooth system 1 (FIG. 22), the adapter nose 2 and complementary socket 3 in the point 4 are wedge-shaped and include converging top and bottom surfaces 2a, 2b, 3a, 3b. A central downward load P applied at the free end 4a of the point 4 will apply a moment force that tends to rotate the point 4 on the nose 2. The load P is generally transmitted to and resisted by the upper side of the nose tip 2c contacting the front end 3c of the socket 3 (reaction force A) and by the lower side of a base portion 2d of the nose contacting the base or rear end 4d of the point 4 (reaction force B). These reaction forces form a counteractive moment to resist the moment formed by force P. As can be appreciated, large vertical forces can create substantial ejection forces. Moreover, the impacts, vibration, wear, and presence of fines, etc. exacerbate the difficulty of resisting high ejection forces.
In the present example of a central downward load P, the vertical component of reaction force A, in general, equals the downward load P plus the vertical component of reaction force B. However, because of the converging walls of the nose, the horizontal component of each of the reaction forces A and B is in a forward direction that tends to urge the point off the nose. To the extent these forces are not resisted directly by the geometry and friction of the nose and socket, they are resisted as shear loads by the lock pin. The repeated application of high shear loads can place unacceptably high stresses on the lock pin and result in its breakage.
Further, in such conventional teeth, the lock pin is typically hammered into place and tightly held by frictional forces applied primarily by the placement of the holes in the point relative to the hole in the adapter nose. However, wearing of the point and adapter will tend to loosen the connection and increase the risk of losing the lock pin. Accordingly, the lock pin is often initially set very tightly in the defined opening so as to put off the time when excessive looseness develops. The lock pin must then be driven into and out of the opening by repeated blows of a large hammer. This can be a troublesome and time-consuming task, especially in the larger sized teeth.
A take-up elastomer has often been placed in front of the lock pin in an effort to maintain a tight fit between the point and adapter when wearing begins to develop. While the elastomer functions to pull the point onto the adapter, it also reduces the lock's ability to resist the applied moment and reverse forces. These loads tend to place more stress on the elastomer than it can withstand. As a result, during use, overworking of the elastomer can result in its premature failure and loss of the lock pin, which then results in loss of the point.
The loss of a point due to pin failure, looseness or elastomer problems not only results in premature loss of the point and wearing of the adapter nose, but also in possible damage to machinery that may be processing the excavated material, particularly in a mining operation. Moreover, since the adapter is often welded in place, replacement of an adapter usually results in significant down time for the digging equipment.
A variety of different point and nose designs have been developed to increase the stability of the point-adapter coupling, reduce the forces tending to eject the point, and lessen loading on the lock.
In one tooth design 1′ (FIG. 23) the front end of the nose 2′ and socket 3′ are each provided with a squared configuration having upper and lower stabilizing flats 5′, 6′. On account of the stabilizing flat 5′, a central downward load P′ on the free end 4c′ of the point 4′ will be transmitted to the nose tip 2a′ so as to generate a vertical reaction force A′ which generally has no substantial horizontal component tending to eject the point from the nose. Nevertheless, the reaction force B′ will still generate a substantial forward horizontal component at the rear of the point that tends to push the point from the nose. While this design improves the stability of the point over the conventional tooth system, it still applies a substantial ejection force and can place high shear forces on the lock.
In another design, such as disclosed in U.S. Pat. No. 5,709,043 to Jones et al., the nose and socket are each provided with a front squared section and rear bearing surfaces that are substantially parallel to the longitudinal axis of the tooth. In this construction, the combined effect of the front stabilizing flats and parallel bearing surfaces create reaction forces at the tip and base of the nose that are generally only vertical. Such vertical reaction forces will in general not generate substantial horizontal components. Accordingly, this construction greatly reduces the forces tending to push the point off of the adapter. Such stabilizing of the point also reduces shifting and movement of the point on the adapter nose for reduced wearing. Nevertheless, multiple other factors (such as impacts, etc.) as well as reverse forces can still apply high shear forces to the lock.
In one other design, such as disclosed in U.S. Pat. No. 4,353,532 to Hahn, the point and adapter are each provided with a helical turn or thread so that the point is rotated about its longitudinal axis when mounted on the adapter nose. On account of the threads, the point rotates about the longitudinal axis of the tooth and generally presses the lock against the adapter nose when ejection forces are applied. The lock is much less likely to fail when under these kinds of compression forces as opposed to the high shear forces applied in conventional teeth. While this construction provides great strength and retention benefits, the nose and socket are complex and more expensive to manufacture.